Hematopoietins, i.e., hematopoietic growth factors, are proteins that promote the survival, growth and differentiation of hematopoietic cells. Colony stimulating factors (CSFs) are a subset of these hematopoietic growth factors that are characterized by the ability to support the growth, in vitro, of colonies of hematopoietic cells arising from progenitor cells of bone marrow, fetal liver, and other hematopoietic organs.
The biochemical and biological identification and characterization of certain hematopoietins has been hampered by the small quantities of the naturally occurring factors available from natural sources, e.g., blood and urine. With recombinant genetic engineering techniques, however, some of these hematopoietins have been molecularly cloned, heterologously expressed and purified to homogeneity. [See D. Metcalf, "The Molecular Biology and Functions of the Granulocyte-Macrophage Colony Stimulating Factors," Blood, 67(2):257-267 (1986).] Among these hematopoietins are human and murine GM-CSF, human G-CSF, human CSF-1 and murine IL-3. Both human GM-CSF [See, R. Donahue et al., Nature, 321:872-875 (1986)] and murine IL-3 [See J. Kindler et al, Proc. Natl. Acad. Sci. U.S.A., 83:1001-1005 (1986), and Metcalf et al., Blood, 68:46-57 (1986)] have a demonstrated effect on hematopoiesis in vivo. The murine protein IL-3 has heretofore been found to have no duplicate in the human system. [See, D. R. Cohen et al, Nucl. Acids Res., 14:3641 (1986).]